1. Field of the Invention
The present invention relates to a wooden connection structure and method of connecting a column and cross beams in a timber construction.
2. Discussion of the Related Art
In general, connecting a column and beam, especially a horizontal timber cross beam, is carried out by a mortise and tenon joint. In case of this joint, the processing of the mortise and tenon joint is carried out by carpenter at a building location, or it is carried out in advance by using a specified machine at a work shop.
In the above mentioned cases, since it requires carpenters having some special skill in the former operation and a specified processing machine in the latter operation, it is difficult to provide an inexpensive timber construction.
Currently known is a connecting structure using a U-shaped metal fitting to connect a column with a cross beam which is disclosed in, for example, Japanese Laid Open Patent Publication No. 8-312007.
In the conventional connecting structure, a U-shaped metal fitting is fixed to the column by bolts through a mortise groove disposed at the side wall of the column. Then the opposite side piece of the metal fitting against the fixed portion to the column is inserted and fixed to a tenon (a slit portion) formed at the side wall of the cross beam.
When a load is transmitted from the cross beam to the column, the column receives a force corresponding to a fiber direction of the column and a parallel direction to the column. The cross beam also receives a force corresponding to a fiber direction of the cross beam and at right-angles to the cross beam.
Assuming that the cross beam has enough strength against a force in the fiber direction in the above prior art, it is described that the metal fitting has a supporting plate welded to the lower edge of the main body of the metal fitting to receive the load of the cross beam.
In other words, the prior art is considered with an external force affecting the cross beam, but it does not consider a load affecting the column at all.
As the result of research by the applicant, it was determined that a force parallel to the fiber direction of the column, causes a relative deformation between the column and the cross beam. Further, it was also learned that the parallel force causes the same effect on the timber construction, when the timber construction receives a large external force. To make sure that the new constructions are earthquake proof, the above problem and external force can not be ignored.
Solutions have been considered to solve these problems. These solutions include selecting a column material from a special material that would be strong against a force in the fiber direction. Secondly, a bolt having a large diameter could be used and thirdly, the number of bolts could be increased.
However, if a special material is used, it is difficult to process the material and it is also expensive. In the second case, using a large diameter bolt should be used with a column having a relatively large cross section considering the increased loss in the cross sectional area of the column and it is also expensive. In the third case, since the space between the bolts becomes relatively thin, the thickness of the fiber disposed in between the bolts is reduced and it is easy for the fiber to collapse.
In other words, since the cross sectional loss of the column caused by the opening for the bolts has a large percentage of the entire cross sectional area of the column, the strength of the column is reduced.
The purpose of the present invention is to provide a solution that does not require complicated processing of the column and cross beam and is without the above mentioned problems. It is also desired to provide a timber construction that is able to receive a relatively large load and is inexpensive to produce.